This application is based on and claims the priority under 35 U.S.C. xc2xa7119 of German Patent Application 100 15 570.7, filed on Mar. 29, 2000, the entire disclosure of which is incorporated herein by reference.
The invention relates to an arrangement for directing both ram air as well as fan-driven air through a heat exchanger that is used for cooling hot compressed air for an air conditioning unit of a passenger transport aircraft.
Modern passenger transport aircraft are typically equipped with air conditioning units, namely so-called air conditioning packs or air generation units. Hot, highly compressed engine bleed air is conveyed to the air conditioning units through suitable conduits or ducts, and in the air conditioning units is then subjected to a combined thermodynamic process generally including cooling by heat transfer through a heat exchanger, followed by compression, further intermediate cooling in a heat exchanger, and finally expansion through a turbine, to ultimately provide air conditioning air at an appropriate pressure and temperature to be introduced into the pressurized cabin of the aircraft.
During this process, which is carried out in an air cycle machine of the air conditioning unit, a substantial proportion of the total heat energy is given off or rejected by heat exchange through one or more air-to-air heat exchangers. Namely, the hot compressed engine bleed air is conveyed through a first heat exchange channel of a heat exchanger core, while a cooling air flow is conveyed through a second heat exchange channel of a heat exchanger core. The first and second heat exchange channels do not allow air flow or air exchange therebetween, but are in a thermal transfer relationship, e.g. thermally conducting, with each other. Thereby, the heat exchange core serves to transfer heat from the hot bleed air or process air to the cooling air flow.
The second channel or cooling air channel of the heat exchanger is connected to an air channel or conduit system which conveys external cooling air from the external environment outside of the aircraft into and through the heat exchanger core, and then exhausts the now-heated cooling air back out to the external environment. In this context, two different air flow conditions must be taken into account. In a first condition, when the aircraft is flying in cruise flight or during take-off and landing at a particular air speed, an inlet channel is arranged in such a manner so that ram air will be introduced into and flow through the heat exchanger. Namely, the aerodynamic pressure difference between the inlet channel and the outlet channel is used as an energy source for driving the cooling air flow through the channel system and through the heat exchanger core.
On the other hand, in a second air flow condition, when the aircraft is parked or taxiing on the ground or in low speed or low altitude flight, whereby nonetheless the air conditioning unit is to be operated to provide air conditioning air, there is insufficient or non-existent ram air flow to provide the required flow rate of cooling air, so it is necessary to mechanically drive an air flow through the heat exchanger using a turbo air machine such as a fan or blower. This turbo air machine may be rotationally driven by a rotating shaft that is driven from any source of rotational power, for example the shaft of an electric motor, or the shaft of the air cycle machine of the air conditioning unit itself.
FIGS. 4 and 5 of the present application show two different conventional cooling air arrangements for conveying cooling air through a heat exchanger of an aircraft air conditioning unit. Particularly, FIG. 4 shows the cooling air arrangement used in the present day Boeing 747 and 777 aircraft, while FIG. 5 shows the cooling air arrangement used in the present day Airbus A340 aircraft. Each of these prior art arrangements includes a cooling air inlet channel 8xe2x80x2 and a cooling air or heat exchanger outlet plenum 4xe2x80x2 with the heat exchanger 1xe2x80x2 interposed therebetween, so that the cooling air A flows from the external environment outside of the aircraft into the inlet channel 8xe2x80x2, through the heat exchanger 1xe2x80x2, and then to the outlet plenum 4xe2x80x2, before being ultimately exhausted back out to the external environment outside the aircraft. Each of the arrangements further includes, as components of or extending from the outlet plenum 4xe2x80x2, a first outlet channel 7xe2x80x2 through which air can be mechanically blown during ground operation of the aircraft, and a second outlet channel 9xe2x80x2 through which ram air flows during flight of the aircraft. In this context, a turbo blower or fan 3xe2x80x2 is driven by the main shaft of the air cycle machine 5xe2x80x2 of the air conditioning unit, and is arranged at an inlet portion of the first outlet channel 7xe2x80x2 so as to suck air from the heat exchanger 1xe2x80x2 and from there through the outlet plenum 4xe2x80x2, and finally blow this air out through the first outlet channel 7xe2x80x2.
The mechanical, structural, aerodynamic, and air flow arrangement and configuration of the several components and particularly the outlet plenum 4xe2x80x2, the first channel 7xe2x80x2, the second channel 9xe2x80x2, and the turbo blower or fan 3xe2x80x2 are very significant and rather complicated to design. Namely, the design and configuration of the arrangements must take into account the two different operating conditions, i.e. air flow conditions, that have been described above, as well as the altitude dependent variation of the air density, the aerodynamic conditions and flow patterns of air outside of the aircraft, the arrangement and orientation of the air cycle machine 5xe2x80x2 relative to the aircraft and relative to the heat exchanger arrangement, and the like. For example, the shaft orientation of the associated air cycle machine that is driving the fan 3xe2x80x2 necessitates an axis-parallel orientation of the heat exchanger arrangement in order to achieve an optimal air flow of the turbo blower or fan 3xe2x80x2. Mounted on the same shaft as the fan 3xe2x80x2, the air cycle machine 5xe2x80x2 includes one or more compressors C and turbines T for compressing and expanding the process air, to ultimately provide the cooled air conditioning air AC from the air outlet 21xe2x80x2. Therefore, the orientation of the installed air cycle machine 5xe2x80x2 is specified based on other considerations, and typically the expansion turbine T and particularly the air conditioning air outlet 21xe2x80x2 of the air cycle machine 5xe2x80x2 must be oriented lying in the flight direction, while the flow of cooling air A being exhausted from the outlet plenum 4xe2x80x2 must be oriented opposite thereto, namely opposite the flight direction of the aircraft.
Taking the above considerations into account, the prior art arrangements of FIGS. 4 and 5 both have an overall air flow pattern of the cooling air A substantially in an S-shape or Z-shape, especially with regard to the fan-driven air flow during ground operation of the aircraft. The conventional arrangements further both use a bypass system in which ram air, to the extent that it is available, will first bypass the first outlet channel 7xe2x80x2 and instead flow directly from the outlet plenum 4xe2x80x2 out through the second channel 9xe2x80x2 to the exhaust outlet. In the conventional Boeing arrangement shown in FIG. 4, this bypass arrangement is achieved with non-return air valves or one-way check valves 2xe2x80x2, and in the conventional Airbus arrangement shown in FIG. 5, this bypass arrangement is achieved with an air injector arrangement 6xe2x80x2 as well as non-return flaps 12xe2x80x2.
In view of the above, the air inlet channel 8xe2x80x2 in the prior art arrangements generally faces forward in the flight direction, while the exhaust air outlet 20xe2x80x2 generally faces rearwardly or downstream relative to the flight direction, as shown in FIGS. 4 and 5. If the conventionally known installation orientation of the equipment is changed, then it may become necessary to achieve a common orientation of the expansion turbine outlet 21xe2x80x2, the heat exchanger inlet 8xe2x80x2, and the outlet plenum exhaust outlet 20xe2x80x2 all facing in the same direction, e.g. in the flight direction. Any attempt to achieve such a configuration or orientation using the cooling air arrangements according to conventional FIGS. 4 and 5 would be impossible or suffer considerable aerodynamic disadvantages, or would simply not be able to achieve acceptable operating characteristics.
Namely, additional air channels as well as air flow redirecting elbows or channel curve members, as well as additional valves or air flaps would have to be provided in the arrangement. This would lead to a disadvantageous increase of the installation size and weight of the overall arrangement, as well as requiring additional maintenance efforts. Also, the aerodynamic efficiency of the cooling air channel directing air through the heat exchanger would be reduced due to the extra air channel components and deflections, and heat exchange energy would thereby be lost. It would also be necessary to increase the size of the various air channel components to try to compensate for such a loss of aerodynamic efficiency, which in turn would result in a greater installation space requirement as well as an increased total weight in the aircraft.
In view of the above, it is an object of the invention to provide a cooling air arrangement for a heat exchanger of an aircraft air conditioning unit with an integrated turbo blower or fan, which achieves a very compact arrangement with an efficient air flow and low flow energy losses, especially for an orientation and arrangement of the components in which the air inlets and air outlet directions face generally in the same direction, and particularly the flight direction of the aircraft. The invention further aims to avoid or overcome the disadvantages of the prior art, and to achieve additional advantages, as apparent from the present specification.
The above objects have been achieved according to the invention in a cooling air arrangement for an aircraft air conditioning unit, comprising a cooling: air inlet channel and a cooling air outlet plenum that are each connected to the external environment outside of the aircraft, and a heat exchanger with second heat exchange passages interposed between the cooling air inlet channel and the cooling air outlet plenum and with first heat exchange passages interposed between a source of hot compressed air such as engine bleed air and the process air inlet of an air cycle machine of the air conditioning unit. According to the invention, the cooling air outlet plenum is divided into or connected to a first outlet channel and a second outlet channel, which will respectively convey the cooling air to the cooling air exhaust outlet dependent on the operating conditions. The second channel extends from the outlet plenum, or substantially forms the outlet plenum, and is connected directly to the outlet side of the heat exchanger. The first channel is branched off of this portion of the second channel in the area of the cooling air plenum, and an outlet end of the first channel then leads back into an air mixing junction or portion of the second channel.
A turbo blower or fan is installed in the inlet area of the first channel, so as to suck cooling air through the heat exchanger during ground operation of the aircraft. On the other hand, during normal flight of the aircraft, ram air is directly driven through the second channel by the pressure difference between the cooling air inlet and the cooling air exhaust outlet. The first channel is particularly provided as a channel in an air guide device which may have an axial, diagonal or radial configuration. For example, the air guide device may comprise a pipe section, a spiral housing, or a plate diffuser respectively defining the first air channel. An air injector or particularly an air injector flap may be arranged between or adjoining the first channel and the second channel in the area of the air mixing junction where the two air channels rejoin each other. This injection flap carries out the function of an injector nozzle or a non-return flap valve depending on the particular operating conditions, so as to allow a proper and compatible air flow of ram air through the second outlet channel and fan-driven air through the first outlet channel.
According to a further detailed feature of the invention, the overall air flow pattern of cooling air through the inventive cooling arrangement is generally a U-shape, namely entering the cooling air inlet from the forward flight direction, then deflecting by substantially a half-turn (e.g. at least 150xc2x0) through the heat exchanger, to then be ultimately discharged through the cooling air exhaust outlet channel in a generally flight forward direction, possibly with further deflection. Thus, the air flow deflection of the entire cooling arrangement is, for example, at least 135xc2x0. The cooling air inlet and the cooling air exhaust outlet channel extending from the present arrangement preferably both are oriented generally toward the forward flight direction, as is the air conditioning air outlet of the air cycle machine of the air conditioning unit.